The invention relates to a control circuit for controlling a liquid crystal display (LCD controller) for two separate bus structures of which one serves for the exchange of data with a computer while the other serves for the exchange of data with at least one addressable memory associated with the liquid crystal display (LCD).
Circuits of this type are known, which make it possible to derive the information-containing signals required to control a liquid crystal display (LCD) module organized in the form of a matrix from a processor system, with the clock pulse and timing control signals for the LCD being generated in the control circuit itself. Most of the characters to be displayed are generated with the aid of memories provided in the control circuit itself which are able, upon an appropriate instruction, to display complete characters on the LCD.
In customary liquid crystal displays with high resolution signal sequences must be produced--corresponding to the matrix-type actuation--which, on the one hand, emit a sequential succession of signal patterns corresponding to image lines and, on the other hand, take care that the characters are newly recorded, for example with the use of the known "two thirds methods", in regular repetition and, additionally, polarity reversals are effected at certain intervals to avoid electrolysis phenomena in the liquid crystal arrangements. Moreover, switching means should be provided, if required, to supply a plurality of the display faces in parallel since the maximum area to be actuated is limited by the repetition intervals to be maintained. The thus generated signals reach the LCD module by way of driver stages.
The drawback is that the prior art control devices for changing the image contents require more or less complicated operations which all have in common that access by the processor to the memory region associated with the LCD is possible only indirectly, after a corresponding request by way of the control circuit, with waiting cycles and similar delays having to be accepted. In other embodiments, the contents of the liquid crystal display can be displayed only indirectly via a memory which itself contains the components required to generate complete characters composed of groups of dots.